A resistive touch panel is widely used as an input unit for a household appliance or a portable terminal because the touch panel is easy to be miniaturized, lightened, and thinned. When a user pushes a part of the touch panel or draws with a specialized pen on a part of the touch panel, the part comes into contact with an opposing electrode, so that the portion and the electrode are electrically connected and a signal is inputted.
As shown in FIG. 4, a typical resistive touch panel has a lower electrode 3 having a glass plate 1 and a transparent conductive layer 2 formed thereon; an upper electrode 6 having a polymer film 4 and a transparent conductive layer 5 formed thereon; and spacers (microdot spacers) 7 interposed between the transparent conductive layers 2 and 5. Pressing the display surface of the upper electrode 6 with a finger or a pen makes the upper electrode 6 and the lower electrode 3 into contact with each other, so that these electrodes are electrically connected and a signal is inputted. The surface of the upper electrode 6 is overlaid with a hard-coating layer 8 for protecting the polymer film 4. Since the surface of the upper electrode 6 is rubbed with a finger or a pen, the upper electrode 6 requires resistance to wear, and therefore is provided with the hard-coating layer 8.
Japanese Patent H2-194943A discloses that after ITO (indium tin oxide) transparent conductive layer is deposited, heat treatment is conducted so as to crystallize ITO, for improving durability of the transparent conductive film for touch panel. However, since the substrate of the transparent conductive film is a polymer film, the temperature for the heat treatment is limited. The heat treatment thus needs to be conducted at relatively low temperature and for a long time, such as at 150° C. and for 24 hours. This causes problems of low productivity and high production cost.
In the touch panel, with the input with a finger or a pen, the transparent conductive layer 5 of the upper electrode 6 and the transparent conductive layer 2 of the lower electrode 3 are contacted and uncontacted repeatedly. The transparent conductive material such as ITO, which is a material for depositing transparent conductive layers 2, 5, has low resistance to wear and indentation. Therefore, in the transparent conductive layer 2 or 5, the transparent conductive layer 5 of the upper electrode 6, which deforms repeatedly during the input to the touch panel, is particularly easy to be cracked. In addition, the transparent conductive layer 5 is easy to be delaminated and removed from the polymer film 4 due to the repeated contact and uncontact between the transparent conductive layers 2 and 5, which are made of the same material.
When the transparent conductive layer 5 of the upper electrode 6 is damaged or delaminated, electrical resistivity of the surface of the transparent conductive layer 5 changes, and uniformity of the electrical resistivity is lost, thereby spoiling electrical properties, and thus the precise input can not be carried out. These cause a decrease in reliability of the touch panel, damages, defects, and a decrease in durability.